Corrosion preventive heatsink for network device

ABSTRACT

In one embodiment, an apparatus includes a chassis base, a printed circuit board mounted on the chassis base, a heatsink positioned over the printed circuit board to prevent corrosion of components on the printed circuit board, wherein the heatsink comprises a plurality of upward extending fins and a plurality of downward extending walls, a seal interposed between an edge of the downward extending walls and the chassis base, and a cover extending over the heatsink.

STATEMENT OF RELATED APPLICATIONS

The present application claims is a continuation of U.S. applicationSer. No. 16/842,505, filed Apr. 7, 2020, which claims priority from U.S.Provisional Application No. 62/915,341, entitled CORROSION PREVENTIVECHASSIS FOR HARSH ENVIRONMENT DEPLOYMENT, filed on Oct. 15, 2019. Thecontents of this provisional application are incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to network devices in acommunications network, and more particularly, to corrosion protectionfor network devices.

BACKGROUND

Network communications systems utilize network devices that includecomplex and sensitive electronic components. The network devices aretypically designed to operate in a controlled environment such as datacenters and central offices with controlled temperature, humidity, andair quality. However, when deployed in harsh environments where there isno control of surrounding air temperature, humidity, and quality, forcedcooled rack mounted equipment may exhibit corrosion induced failures,which results in service interruption.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an exploded perspective of a corrosion preventive heatsink,printed circuit board, and chassis base, in accordance with oneembodiment.

FIG. 2 is a top view of the chassis base with the printed circuit boardand heatsink removed.

FIG. 3 is a side view of the heatsink installed over the printed circuitboard on the chassis base.

FIG. 4A is a cross-sectional front view of the heatsink installed overthe printed circuit board on the chassis base.

FIG. 4B shows is a cross-sectional front view showing an enlargedportion of the heatsink, printed circuit board, and chassis base shownin FIG. 4A.

FIG. 5 is a cross-sectional perspective showing a portion of theheatsink, printed circuit board assembly, and chassis base.

FIG. 6 is an exploded perspective of a chassis showing the heatsink andprinted circuit board along with fans and power supplies.

FIG. 7 is a perspective of the assembled chassis of FIG. 6 without thechassis cover.

FIG. 8 is a perspective of the assembled chassis.

FIG. 9 is a block diagram depicting an example of a network device inwhich the embodiments described herein may be implemented.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

In one embodiment, an apparatus generally comprises a chassis base, aprinted circuit board mounted on the chassis base, a heatsink positionedover the printed circuit board to prevent corrosion of components on theprinted circuit board, wherein the heatsink comprises a plurality ofupward extending fins and a plurality of downward extending walls, aseal interposed between an edge of the downward extending walls and thechassis base, and a chassis cover extending over the heatsink.

In one or more embodiments, the apparatus further comprises a fanpositioned on the chassis base for generating airflow across the fins ofthe heatsink.

In one or more embodiments, the heatsink and chassis base define sealedcavities above the printed circuit board and below the printed circuitboard.

In one or more embodiments, an inner edge of the heatsink defines ashoulder engaged with an upper side of the printed circuit board.

In one or more embodiments, the apparatus further comprises a thermalpad interposed between an internal surface of the heatsink and a chipmounted on the printed circuit board.

In one or more embodiments, the heatsink generally extends along anentire width of the chassis base.

In one or more embodiments, the seal comprises a U-shaped gasketcomprising one or more sealing elements.

In one or more embodiments, a front edge of the heatsink is in directcontact with an optical module port.

In another embodiment, an apparatus generally comprises a chassis base,a printed circuit board mounted on the chassis base, a plurality of fansmounted on the chassis base, and a heatsink positioned over the printedcircuit board to prevent corrosion of the printed circuit board. Theheatsink comprises a plurality of fins positioned to allow airflowgenerated by the fans to flow across the fins.

In yet another embodiment, an apparatus generally comprises a chassisbase, a printed circuit board mounted on the chassis base, and aheatsink positioned over the printed circuit board. The heatsinkcomprises a rear wall and side walls for creating a seal with thechassis base and a front opening for receiving an optical module cagemounted on the printed circuit board to protect the printed circuitboard from corrosion and provide cooling to the printed circuit boardand an optical module inserted into the optical module cage.

Further understanding of the features and advantages of the embodimentsdescribed herein may be realized by reference to the remaining portionsof the specification and the attached drawings.

Example Embodiments

The following description is presented to enable one of ordinary skillin the art to make and use the embodiments. Descriptions of specificembodiments and applications are provided only as examples, and variousmodifications will be readily apparent to those skilled in the art. Thegeneral principles described herein may be applied to other applicationswithout departing from the scope of the embodiments. Thus, theembodiments are not to be limited to those shown, but are to be accordedthe widest scope consistent with the principles and features describedherein. For purpose of clarity, details relating to technical materialthat is known in the technical fields related to the embodiments havenot been described in detail.

Network communications devices are increasingly being used inuncontrolled or partially uncontrolled environments that have differentconditions than a data center or central office. In many of thesedeployments, the network device has no environmental protection (or onlypartial protection) and may be directly exposed to ambient air. Based onthe climatic conditions of the area, the ambient air may not only carrya lot of dust and moisture, but also different chemical compounds. Thenetwork device may be subjected to adverse environmental factorsincluding temperature and humidity extremes, airborne particulates,chemical pollutants, and other contaminants. The environment in whichthe network device operates may not be conducive to prolonged operationand life of the equipment. For example, when deployed in harshenvironments (e.g., no air conditioning or filter cabinets) with highhumidity, hygroscopic dust, and salt fog, rack mountable equipment mayseverely suffer from corrosion related failures.

Although all types of outdoor equipment face these issues, the severityof the failure is typically higher for forced air cooled devices due tothe high flow rate of contaminated air within equipment enclosures. In aforced air cooled network device, the contaminants in the air may reactwith metal used in electronic components and cause corrosion. Deploymentof network devices in the presence of uncontrolled contamination incooling air (e.g., dust, moisture, abrasive chemicals, water solublesalts, etc.), may lead to damage of the components. Failure of thenetwork device or components may occur very quickly in an uncontrolledenvironment. These failures are not predictable and therefore createservice interruption and high costs for replacement units. Since thesefailures are often not recoverable, the downtime associated with thesefailures may be significant.

One method for protecting components from corrosion is a conformalcoating process that coats a printed circuit board assembly with a thinfilm for protection of surface mounted components from corrosion.However, conformal coatings may not reduce corrosion to a desired level.For example, hygroscopic dust and salt fog combined with high airvelocity from cooling fans may erode the conformal coating and allowcorrosion to start. Moreover, when the conformal coating is applied,reworking of components becomes difficult and units may need to bereplaced, rather than repaired.

In harsh environments such as cell towers with high humidity,hygroscopic dust, salt fog, and high velocity air, the only way toprotect a printed circuit board assembly from corrosion is to isolate itfrom the corrosive environment. As the conventional method of conformalcoating does not work well, it is important to provide isolation withoutjeopardizing thermal performance,

The embodiments described herein provide a corrosion preventive heatsinkthat eliminates (or reduces) a need for a conformal coating, thusallowing printed circuit boards to be easily reworked. Furthermore, asdescribed in detail below, the heatsink is configured to operate in afan assisted environment, thus providing additional cooling. Since theheatsink allows for a reduction in the air passing through the chassis,corrosion on non-sealed parts of the chassis due to contaminants,hygroscopic dust, high humidity, and possible high salt in the humid airin coastal regions is also reduced.

Referring now to the drawings, and first to FIG. 1, a large heatsink(sealing heatsink, corrosion preventive heatsink) 10 configured to seala printed circuit board (PCB) (also referred to herein as a PCBA) 12including both component (upper side of PCB as viewed in FIG. 1) andsolder (lower side of PCB) is shown. As described in detail below, theheatsink 10 engages with a chassis base 14 and a port assembly (opticalmodule ports, optical module cages, cage assembly, Ethernet ports) 16 tocover, seal, and protect the entire PCB 12, thereby eliminating (orreducing) the need to apply conformal coatings to the PCB.

The heatsink 10 is positioned over the printed circuit board 12 toprevent corrosion of the printed circuit board (i.e., printed circuitboard and components mounted on the printed circuit board). As shown inthe example of FIG. 1, the heatsink 10 comprises a plurality of upwardextending fins 15 and a plurality of downward extending walls (rear walland side walls) 30. A seal 18 is interposed between a periphery edge ofthe downward extending walls 30 and the chassis base 14. As describedbelow with respect to FIG. 6, a cover extends over the heatsink 10. Theheatsink 10 generally extends the entire width of the chassis base 14(from front to rear as viewed in FIG. 1).

As shown in FIG. 1, a natural convection cooling style heatsink 10 ispositioned to mate with the chassis base 14 and cover the entire PCB(PCBA) 12. As described below, a front portion (as viewed in FIG. 1) ofthe heatsink 10 mates with one or more port assemblies 16 positioned ona front edge of the printed circuit board 12 for receiving opticalmodules (transceiver modules) or plugs. One or more seals (sealinggasket) 18 positioned on the base 14 of the chassis allow the heatsink10 to create sealed cavities above and below the PCB 12, as describedbelow with respect to FIGS. 4 and 5.

The heatsink 10 includes a plurality of fins 15, which allows excessthermal energy to dissipate into the environment by convection. Theheatsink 10 is configured to maximize the surface area in contact with acooling medium (e.g., air) surrounding the heatsink. The heatsink 10 maybe die cast or formed from any other suitable process and any suitablematerial (e.g., aluminum, copper, or other material) having relativelyhigh heat conduction characteristics to allow heat transfer fromelectronic components mounted on the PCB 12 and optical modules insertedinto the optical module cages 16 to the heatsink 10. The heatsink 10 mayhave any shape (e.g., height, width, length, ratio of width to length,footprint) and any number, size, or configuration of fins 15. Theheatsink 10 is sized to fit over the PCB 12 and components mounted onthe PCB, as shown in FIG. 1.

The fins 15 are positioned to allow air flow from the fans to passbetween aligned rows of the fins (air flow in-line with fins). Asdescribed below, one or more fans are positioned on the chassis base forgenerating airflow across the fins 15 of the heatsink 10. The forcedairflow over the fins 15 further increases cooling. As discussed below,the additional cooling provided by the heatsink 10 may reduce the needfor operation of the fans (reduced speed or reduced operation time),thereby saving power and further reducing contamination of unsealedcomponents (e.g., power supply or circuit components not located underthe heatsink 10) by reducing the amount of air (with possiblecontaminants) passing through the chassis at a high velocity. Forexample, the fans may be stopped below a specified temperature withinthe chassis in which the heatsink 10 provides sufficient cooling. Thefans may also operate at a reduced speed (revolution per minute (RPM))based on cooling provided by the heatsink 10.

As described below, walls 30 of the heatsink 10 extend downward on threesides (rear and opposing sides) of the heatsink to mate with the seal(gasket) 18 on the base 14. An opening (U-shaped opening) 13 is definedalong a front edge of the heatsink 10 to allow an upper surface of theheatsink to engage with components (optical module cages, ports, orother port assembly 16) mounted along a front edge of the PCB 12 andfurther enclose the sealed cavities (created by the heatsink walls 30and seal 18 on the chassis base 14) to protect the PCB from corrosion.The front portion of the heatsink positioned over the port assemblies 13may provide additional cooling to optical modules inserted into theoptical module cage 16.

The printed circuit board assembly 12 may comprise any number ofelectronic components (circuits, chips, die, etc.). The printed circuitboard 12 provides a dielectric material for copper or other conductivetraces. The traces and pads are embedded within or deposited on theprinted circuit board 12 for connection with the electronic components.Etching, deposition, bonding, or other processes may be used to form thetraces, pads, or embedded components (e.g., passive or active devices).The printed circuit board may 12 include one or more active devices(e.g., transistor, chip, processor, circuit, application specificintegrated circuit, field programmable gate array, memory, etc.) and oneor more passive devices (e.g., capacitor, resistor, inductor, connector,via, pad, etc.). The traces, pads, and electronic components may bearranged in any configuration to perform any number of functions foroperation on any type of network device (e.g., computer, router, switch,server, gateway, controller, edge device, access device, aggregationdevice, core node, intermediate node, or other network device). It is tobe understood that the term ‘printed circuit board’ or ‘printed circuitboard assembly’ as used herein refers to a substrate, circuits, andcomponents mounted on the substrate.

The chassis base 14 includes a lower surface 21 and a rear wall 23 andside walls 25 extending upward from the lower surface. The side walls 25include openings 17 to allow air to flow (e.g., airflow generated byfans) through the chassis. The side walls 25 may also include any numberof openings 27 for receiving fasteners for attaching a chassis cover tothe base 14. The lower surface 21 may also include openings 26 forreceiving fasteners (e.g., screws) for attaching the heatsink 10 to thechassis base 14. As shown in FIG. 1, the PCB 12 may have recesses(notches) 19 formed along one or more edges to provide room for thefasteners.

FIG. 2 is a top view of the chassis base 14 of FIG. 1 with the PCB 12and heatsink 10 removed to show details. In the example shown in FIG. 2,the chassis base 14 comprises a plurality of grooves or channels 20 forreceiving one or more seal (gasket) 18. The gasket 18 is positioned toseal the cavity under the heatsink 10 on the chassis base 14 where thePCB 12 sits, as described below with respect to FIGS. 4 and 5. The seal18 is positioned to engage with a periphery edge of the heatsink 10defined by walls 30 (FIG. 1) that mate with the chassis base 14. In theexample shown in FIG. 2, the seal 18 comprises a U-shaped gasketcomprising one or more sealing elements. As described above with respectto FIG. 1, port assemblies 16 are mounted on a front edge of the PCB 12,thus there is no seal positioned along the front edge of the chassisbase 14. The port assemblies 16 and mating heatsink create a frontenclosure for the PCB and components rearward of the port assemblies.Since forced airflow enters along a side edge of the heatsink, the sealcreated by the gasket 18 interposed between the side wall 30 of theheatsink and the chassis base 14 is important in preventing contaminantsfrom entering the enclosure.

The PCB 12 is positioned on the chassis base 14 in a first portion ofthe base (indicted at 24) internal to the seal 18 (FIGS. 1 and 2). Asdescribed below with respect to FIGS. 6 and 7, one or more fans andpower components (e.g., power supply units) are positioned in a secondportion 28 of the base. The fans provide airflow across the heatsink 10when additional cooling is needed.

FIG. 3 is a side view of the heatsink 10 installed on the chassis base14. The heatsink 10 includes the fins 15 extending upward (as viewed inFIG. 3) and side walls 30 extending downward for engagement with thechassis base 14. An enlarged view in FIG. 3 illustrates an interfacebetween the heatsink 10 and chassis base 14. As previously describedwith respect to FIGS. 1 and 2 a periphery seal (gasket) 18 is interposedbetween the heatsink wall 30 and chassis base 14.

FIGS. 4A and 4B illustrate a cross-sectional front view of the assembledheatsink 10, PCB 12, and chassis base 14. FIG. 4B shows an enlarged viewof the cross-section shown in FIG. 4A. As previously described, the seal18 is interposed between a lower edge 48 of wall 30 of the heatsink 10and the chassis base 14. The heatsink 10 and the chassis base 14 definesealed cavities above the printed circuit board and below the printedcircuit board. As shown in FIG. 4B, the heatsink 10 forms sealed cavity40 on an upper surface of the PCB 12 and sealed cavity 42 on a lowersurface of the PCB. An inner edge of the heatsink defines a continuousshoulder (shown at 46) that engages with an upper side (component side)of the printed circuit board 12 to provide additional sealing (alsoshown in FIG. 5).

FIG. 5 is a perspective cross-sectional view of the assembled heatsink10, PCB 12, and chassis base 14 shown in FIG. 4A. Sealed cavity 40defined by the heatsink 10 and the upper surface of the PCB 12 andsealed cavity 42 defined by the lower surface of the PCB and the chassisbase 14 are shown in FIG. 5. As previously noted, any number or type ofcomponents (e.g., circuits, chips, die) may be mounted on the uppersurface of the PCB 12. FIG. 5 shows an ASIC (Application SpecificIntegrated Circuit) 50 mounted on the PCB 12 and a high performancethermal gap pad 52 interposed between a lower surface of the heatsink 10and the ASIC. In one example, the heatsink may 10 be configured for usewith any number of thermal pads for providing direct contact betweenASICs (or other components) and the heatsink for increased cooling ofthe ASICs.

FIG. 6 is an exploded view of a chassis 60, in accordance with oneembodiment. The chassis may comprise, for example, a 1RU (Rack Unit)rack mounted chassis and may be configured for operation as a router,switch, or any other network device. The chassis includes the base 14, acover 62, and a face plate 64. The face plate includes a number ofopenings for providing access to ports (receptacles, port assemblies) onthe chassis 60. The cover 62 includes an upper surface 61 and walls 63extending downward from the upper surface for alignment with walls 24 ofthe chassis base 14. The cover 62 may be fastened to the lower base 14with any number of fasteners inserted into aligned openings in the coverand base. The side walls 63 of the cover 62 include openings 65 to allowairflow to pass therethrough. The chassis 60 further includes one ormore fans (fan assemblies) 66 and power components (e.g., power supplyunits) 68. In one example, the fans 66 pull air through the chassis (airflow direction from right to left of chassis 60 as viewed in FIG. 6). Aspreviously noted, the fins 15 of the heatsink 10 are aligned with thefans 66 such that airflow passes across the fins.

FIG. 7 is a perspective view of the assembled chassis with the cover 62removed to show details of the heatsink 10, fans 66, and power supplyunits 68. FIG. 8 is a perspective of the chassis 60 with the cover 62installed. As shown in FIG. 8, the assembled chassis 60 includes aplurality of ports 80 for receiving modules or plugs.

It is to be understood that the arrangement shown in FIGS. 1-7 is onlyan example and the sealing heatsink (corrosion preventive heatsink) 10described herein may be used in other types of network devices (chassis)with different size or shape PCB (PCBA), or a different number, type, orarrangement of components (e.g., fans, power supply units, portassemblies, circuits, chips). Also, it is to be understood that theterms upper, lower, above, below, rear, front, back, and the like asused herein refer to the views shown in the drawings and may bedifferent than described herein based on the position of the chassis.

In one or more examples, the equipment may be configured to be GR-3108(Generic Requirements for Network Equipment in the Outside Plant)Class-3 compliant (and in some cases it may be worse than the standarddue to customer installation requirements). In one or more embodiments,the equipment may be configured to operate up to 70° C. (300 m altitude)and include multiple fans to augment cooling at such temperatures,regardless of the cooling capacity of the corrosion preventive heatsink.Depending on the power dissipation of the printed circuit boardassembly, fans may not be working up to a certain temperature or theremay be up to 30° C. inlet temperature, for example, and the fans mayturn at minimum speed for increased reliability. This also allows thefans to consume very low power (e.g., less than 2 watts).

In one example, the embodiments described herein operate in the contextof a data communications network including multiple network devices. Thenetwork may include any number of network devices in communication viaany number of nodes (e.g., routers, switches, gateways, controllers,edge devices, access devices, aggregation devices, core nodes,intermediate nodes, or other network devices), which facilitate passageof data over one or more networks. The network devices may communicateover or be in communication with one or more networks, which may includeany number or arrangement of network communications devices (e.g.,switches, access points, routers, or other devices) operable to route(switch, forward) data communications. The embodiments described hereinmay be implemented, for example, in a rack mounted network device.

FIG. 9 illustrates an example of a network device 90 (e.g., chassis 60)that may implement the embodiments described herein. In one or moreembodiments, the network device 90 is a programmable machine that may beimplemented in hardware, software, or any combination thereof. Thenetwork device 90 includes one or more processor 92, memory 94, networkinterface (port) 96. One or more of these components may be mounted onprinted circuit board 98. As previously described, the printed circuitboard and components are protected by the sealing heatsink (corrosionpreventive heatsink). One or more of the processor 92, memory, 94, andnetwork interfaces 96 may be mounted on the printed circuit board.

Memory 94 may be a volatile memory or non-volatile storage, which storesvarious applications, operating systems, modules, and data for executionand use by the processor. The network device may include any number ofmemory components (e.g., chips) 94 that may be protected from corrosionusing the embodiments described herein.

Logic may be encoded in one or more tangible media for execution by theprocessor 92. For example, the processor 92 may execute codes stored ina computer-readable medium such as memory. The computer-readable mediummay be, for example, electronic (e.g., RAM (random access memory), ROM(read-only memory), EPROM (erasable programmable read-only memory)),magnetic, optical (e.g., CD, DVD), electromagnetic, semiconductortechnology, or any other suitable medium. In one example, thecomputer-readable medium comprises a non-transitory computer-readablemedium. The network device 90 may include any number of processors. Inone or more embodiments, logic may control operation (e.g., speed) ofthe cooling fans based on system temperature, for example. The PCB 98may include any number of processors (e.g., circuits, chips, die) andmay include a controller (e.g., software, code) operable to control fanspeed based on measured operating temperature. As previously described,the corrosion preventive heatsink 10 may allow reduced speed oroperation of the fans by providing increased cooling to the PCB.

The network interface may comprise any number of interfaces (line cards,ports, optical module cages) for receiving data or transmitting data toother devices.

It is to be understood that the network device shown in FIG. 9 anddescribed above is only an example and that different configurations ofnetwork devices may be used. For example, the network device may furtherinclude any suitable combination of hardware, software, algorithms,processors, devices, components, or elements operable to facilitate thecapabilities described herein. Also, it is to be understood that theembodiments described herein are not limited to use in a network deviceand may be used in any type of electronic equipment with components thatare susceptible to corrosion.

As can be observed from the foregoing, the embodiments may be used toeliminate (or reduce) conformal coatings on a printed circuit boardwithout increasing corrosion related failures in harsh environments,thereby saving costs on rework and initial manufacturing, while reducingservice interruption. In one or more embodiments, manufacturing andproduct costs are reduced by eliminating (or reducing) conformalcoatings, which allows the printed circuit board assemblies to bereworked. Overall system reliability may be increased due to increasedMTBF (Mean Time Between Failure), allowing less service disruptions andimproved user experience. Also, operating costs may be reduced bybalancing natural and forced convection. For example, below a certainthreshold temperature fans may not need to work, and above the thresholdtemperature fans may run at a lower speed (RPM) than conventional forcedair cooling systems. By reducing or completely stopping one or morefans, accumulation of hygroscopic dust, which is one of the maincontributors of corrosion, is minimized inside the chassis. Similarly,by reducing the amount of air passing through the unit, corrosion onnon-sealed parts of the chassis due to contaminants, high humidity andpossible high salt in the humid air in coastal regions in addition tohygroscopic dust is also reduced.

Although the method and apparatus have been described in accordance withthe embodiments shown, one of ordinary skill in the art will readilyrecognize that there could be variations made without departing from thescope of the embodiments. Accordingly, it is intended that all mattercontained in the above description and shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:
 1. An apparatus comprising: a chassis base; aprinted circuit board mounted on the chassis base; a heatsink positionedover the printed circuit board to prevent corrosion of the printedcircuit board, wherein the heatsink comprises a plurality of upwardextending fins and a plurality of downward extending walls; powercomponents mounted on the chassis base adjacent to the heatsink; a sealinterposed between an edge of the downward extending walls and thechassis base; and a chassis cover extending over the heatsink.
 2. Theapparatus of claim 1, further comprising a fan positioned on the chassisbase for generating airflow across the fins of the heatsink.
 3. Theapparatus of claim 1, wherein the heatsink and the chassis base definesealed cavities above the printed circuit board and below the printedcircuit board.
 4. The apparatus of claim 1, wherein an inner edge of theheatsink defines a shoulder engaged with an upper side of the printedcircuit board.
 5. The apparatus of claim 1, further comprising a thermalpad interposed between an internal surface of the heatsink and a chipmounted on the printed circuit board.
 6. The apparatus of claim 1,wherein the heatsink generally extends along an entire width of thechassis base.
 7. The apparatus of claim 1, wherein the power componentsare configured to provide power to a fan.
 8. The apparatus of claim 1,wherein the seal comprises a U-shaped gasket comprising one or moresealing elements.
 9. An apparatus comprising: a chassis base; a printedcircuit board mounted on the chassis base; a plurality of fans mountedon the chassis base; and a heatsink positioned over the printed circuitboard to prevent corrosion of components on the printed circuit board,wherein the heatsink comprises a plurality of fins positioned to allowairflow generated by the fans to flow across the fins; wherein an inneredge of the heatsink defines a shoulder that is engaged with an upperside of the printed circuit board.
 10. The apparatus of claim 9, whereinthe plurality of fans are stopped below a specified temperature withinthe chassis in which the heatsink provides sufficient cooling.
 11. Theapparatus of claim 9, wherein the plurality of fans operate at a reducedrevolution per minute based on cooling provided by the heatsink.
 12. Theapparatus of claim 9, wherein the heatsink comprises a plurality ofdownward extending walls and a seal interposed between an edge of thedownward extending walls and the chassis base.
 13. The apparatus ofclaim 9, wherein the heatsink and the chassis base define sealedcavities above the printed circuit board and below the printed circuitboard.
 14. An apparatus comprising: a chassis base; a printed circuitboard mounted on the chassis base, the printed circuit board includingat least one chip mounted thereon; a plurality of fans mounted on thechassis base; a heatsink positioned over the printed circuit board toprevent corrosion of components on the printed circuit board, whereinthe heatsink includes an internal surface and comprises a plurality offins positioned to allow airflow generated by the fans to flow acrossthe fins; and power components mounted on the chassis base adjacent tothe heatsink; a thermal pad interposed between the internal surface ofthe heatsink and the at least one chip.
 15. The apparatus of claim 14,wherein the heatsink generally extends along an entire width of thechassis base.
 16. The apparatus of claim 14, further comprising anoptical module cage mounted on the printed circuit board, and whereinthe internal surface of the heatsink engages with the optical modulecage to enclose a sealed cavity defined by the heatsink and the chassisbase.
 17. The apparatus of claim 16, wherein the heatsink comprises arear wall and side walls that form a seal with the chassis base.
 18. Theapparatus of claim 17, wherein the seal further comprises a gasketinterposed between the walls of the heatsink and the chassis base. 19.The apparatus of claim 16, wherein the heatsink is configured to protectthe printed circuit board from corrosion and provide cooling to theprinted circuit board and to an optical module inserted into the opticalmodule cage.
 20. The apparatus of claim 14, wherein the plurality offans are stopped below a specified temperature within the chassis inwhich the heatsink provides sufficient cooling.